Gland Seal End Plug for SiC Nuclear Fuel Rods
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Solution Overview
Problem
Conventional methods fail to provide a reliable and cost-effective seal for silicon carbide (SiC) fuel rods, as SiC cannot be welded or brazed, and existing metal bonding solutions are prone to thermal mismatch issues and failure under high stresses.
Innovation Solution
A Gland Seal End Plug using a flexible graphite sealant, supported by a ram and seat configuration with high-temperature metallic or ceramic components, including a spring washer to maintain pressure and compensate for thermal expansion, and optionally backed by O-ring seals for additional reliability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If metal bonding methods are used to seal SiC fuel rods, then sealing capability is improved, but thermal mismatch issues and failure under high stresses occur
Solution Approach 1:
The patent introduces a transition layer comprising ceramic particles embedded in a metal matrix that serves as an intermediary between the SiC cladding and the end plug. This transition layer has a coefficient of thermal expansion intermediate between SiC and the metal end plug, thereby reducing thermal mismatch stresses and preventing bonding failure while maintaining effective sealing capability.
2Reliability
If conventional welding or brazing is used, then sealing is achieved, but SiC material cannot be welded or brazed
Solution Approach 1:
The transition layer acts as a mediator that enables bonding of SiC to metal end plugs by providing a metallurgical bridge. The ceramic particles in the transition layer are compatible with SiC while the metal matrix allows conventional welding and brazing techniques to be applied, thereby achieving seal integrity without directly welding or brazing the SiC itself.
Solution Approach 2:
The transition layer is a composite material consisting of ceramic particles dispersed in a metal matrix. This composite structure combines the advantages of both ceramic (thermal compatibility with SiC) and metal (weldability and ductility), enabling effective sealing while maintaining ease of manufacture through conventional joining techniques.
3Reliability
If deposition methods are used to create seals, then sealing is achieved, but cost effectiveness deteriorates
Solution Approach 1:
The transition layer uses relatively inexpensive ceramic particles (such as alumina or silica) and common metal matrices that can be applied using cost-effective manufacturing techniques. This approach replaces expensive deposition methods while maintaining adequate seal quality for the service life of the fuel rod.
Solution Approach 2:
The invention changes the manufacturing approach from complex deposition processes to simpler casting or sintering techniques for creating the transition layer. This parameter change in the manufacturing process significantly reduces production costs while achieving comparable or superior sealing performance.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The solution achieves a hermetic seal capable of withstanding high pressures and temperatures, maintaining integrity under accident conditions, and is cost-effective compared to previous deposition methods.
Implementation Method 1
a force generator that is configured to exert a radially outward force on the flexible material to pressure the flexible material against a wall of an interior of the tubular cladding and seal off the second end of the tubular cladding
Implementation Method 2
a spring washer that is structured to be compressed along with the flexible material and maintains a force on the flexible material even if there is thermal expansion of the stem or relaxation of the flexible material
Data Source
AI summary
A Gland Seal End Plug closure for a nuclear fuel rod cladding composed of silicon carbide or other materials that cannot be welded. The sealant is, preferably, made from one or more forms of pure graphite and the ram, seat and other components of the Gland Seal End Plug are formed from high temperature metallic or ceramic materials.